The invention relates to a method of manufacturing a metal matrix for use in the manufacture of optical discs in which a master plate, which comprises a substrate and a photosensitive recording layer provided thereon is exposed to modulated laser light, in which an information track having a relief structure is formed in the recording layer, the recording layer is provided with a metal layer first by electroless plating and then by electrodeposition, and the resulting metal matrix in which the information track of the master has been copied is separated from the master.
Such a method is known from European Patent Specification 0 022 313. According to this method a master plate is used in the manufacture of a metal matrix the recording layer of which comprises an explosive material, for example nitrocellulose, if desired in combination with a dye. Upon exposure to modulated laser light incomplete explosions are induced (column 7 of EU-PS 0 022 313) as a result of which gases are formed which do not escape but remain enclosed in the material. As a result of the gas pressure bumps are formed in the exposed places. Optionally, a metal layer may be provided over the explosive recording layer in which bumps are also formed as a result of the incomplete explosions which take place in the underlying recording material.
The disadvantage of the known method is that the formation of bumps is a critical process. This means that as a result of small local deviations in the composition of the explosive recording layer and/or local differences in thickness as a result of which, for example, the thermal conductivity varies locally, the induced explosions can easily lead to the formation of holes instead of the desired bumps. The size of the bumps may also vary locally as a result of the deviations mentioned hereinbefore. Another disadvantage is that it is not possible when using the known process to induce bumps which, while having the same width dimension, have different accurately defined longitudinal dimensions. Information bits (bumps) with accurately adjusted longitudinal dimensions, for example, longitudinal dimensions of 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7 and 3.0 .mu.m, are necessary for the recording of information which is modulated according to the EFM (eight out of fourteen modulation) system.